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As fledgling conservation students, we are encouraged to get a
good grounding in the techniques, tools and materials that were
used to make the original objects that we now conserve. For
example, we use hide glue for making glued joints, wooden moulding
planes for making specific profiles and hand tools such as chisels,
planes and saws for shaping wood or metal.

We are also meant to pick up some historical context for the
items that we deal with. We learn about historical makers, trends
in design, and how notable objects have been conserved and
repaired. However, there is one important piece of historical
context that is not often emphasised - and this is the measurement
system.

Most people know that the metric system was introduced in
France, associated with the whirlwind of new legislation and
standards that followed the French Revolution. However, it is less
obvious why this occurred, and why it occurred in France rather
than in England or elsewhere.

In England, the system of measurement had been unitary more or
less since the Magna Carta, which had decreed that 'There shall be
one unit of measure throughout the realm'. A significant amount of
effort by local government went into policing this, mainly to
ensure that people were not sold short weight or volume.

In France, on the other hand, the system of measurement handed
down from Charlemagne had fractured into many hundreds of competing
units by the eighteenth century, which meant that different regions
of France would mean very different things by what should be
standard measures of weight, distance or volume. Clearly then,
there was a pressing need for the metric system in France, much
less of a need in England. For this reason, metrication came late
to Britain and it can safely be assumed that many of the items we
will be called upon to conserve would originally have been made in
feet and inches.

One notable thing about using imperial measures is the tendency
to select simple ordinal points (inches, half inches, quarter
inches) when designing anything. As a case in point, a recent
project to copy a nest of tables derived a set of measurements for
the table leg, giving a set of measurements in millimetres that
were precise but with no obvious relationship between them. On
checking the measurements in inches, however, it became evident
that all of them were done to the nearest quarter-inch (e.g 4",
41/4", etc) and that all the beadings were quarter inch in
size.

Knowing this serves two purposes. Firstly, it gives insight into
the design process, which will often select a measurement to the
nearest inch or half inch rather than an arbitrary number of
millimetres. Secondly, it allows us to recover information.

Rather like making a photocopy, any copying process (mechanical
or otherwise) can lead to degradation of the original form and loss
of information. If it is known, however, what the original
measurements were meant to be, then an accurate version of the
original can be made, with no errors - this will be a re-creation
rather than a copy.

This is not an argument for going back to the imperial system.
Anyone who has spent time in the engineering industry will
recognise what a retrograde step this would be. However, there is
an argument for being aware of it, understanding its place in
design history, and being familiar with the units that form an
integral part of the design of so many pieces.

As a first step, the aspiring imperial student should learn to
recognise some common measurements and their metric
equivalents.

If it looks like...

Then it's probably ..

300 mm

One foot (12 inches) (304.8 mm)

150 mm

Six inches (152.4 mm)

75 mm

Three inches (76.2 mm)

25 mm

One inch (25.4 mm)

19 mm

¾ inch (19.05 mm)

12 / 13 mm

½ inch (12.7 mm)

6 mm

¼ inch (6.3mm)

Acres, poles, rods, perches, chains, furlongs, bushels, hogsheads
and firkins will be left to a future essay!